(I would assume singing...but the OP can clarify.) I typically only do that in particularly knotty passages where one can get lost more readily*, but then again I trained as a horn player, and horn players in grade school get *drilled* like percussionists in playing on the off-beats so that it becomes second nature (to this day, decades later, if I am subjected to some relentlessly on-beat music, I naturally start grunting or breathing off-beat. And do not get me started on people who clap only on the beat....).

* Two examples that come readily to mind are: the tenor line in the Alleluias of Handl/Gallus' "Ab Oriente Venerunt Magi" and the tenor line in the Deo gracias of Boris Ord's setting of "Adam Lay Ybounden." Some passages in Byrd's more syncopated passages, too. And sometimes in long runs of, for example, Schutz, Bach or Handel, just to remind me to shape/inflect them more.

Hey, another horn player! I had the exact same experience, and will clap off-beat just because I can. My family is not impressed.

Carl D

And all those etudes....

Which reminds me: that's something that people who trained in instruments appear to be more used to than choristers - the rigor of successive volumes of etudes (when "mastered," you reprise from the beginning...). Not quite the same thing as warming up exercises and vocalises.